Method for adjusting the phase-locking loop of an electronic evaluation device and corresponding electronic evaluation device

ABSTRACT

A method is described for balancing the phase-locked loop of an electronic analyzing device which analyzes the output signal of a sensor device, a yaw rate sensor in particular using the Coriolis effect having an oscillating mass which undergoes a deflection under the effect of an external yaw rate on the sensor device and the output signal representing a yaw rate signal, the electronic analyzing device having in addition to the phase-locked loop, a control loop, a quadrature control loop in particular, and the control loop is provided with a controller having an input and an output as well as with a modulator or mixer having an input which has a first electrical connection with the output of the controller. In order to reduce the percentage of sensor devices produced which, however, cannot be balanced the first electrical connection is interrupted between the output of the controller and the input of the mixer and a second electrical connection is produced between the output of the controller and the input of the mixer, the second electrical connection being made by connecting an attenuating element in between.

FIELD OF THE INVENTION

The present invention relates to a method for balancing the phase-lockedloop of an electronic analyzing device and an electronic analyzingdevice.

BACKGROUND OF THE INVENTION

Yaw rate sensors that utilize the Coriolis effect (so-called Coriolisvibratory gyros or abbreviated: CVGs) have an oscillating mass (sensorelement) and an electronic analyzing circuit by which the deflection ofthe oscillating mass is determined based on the effect of an externalyaw rate on the sensor. The electronic analyzing circuit is typicallyprovided with a phase-locked loop (PLL) to obtain information concerningthe phase position of path-proportional and velocity-proportionalsignals. Furthermore, the PLL synchronizes the signal processing withthe sensor drive frequency.

The following is true of the Coriolis force F_(C):

F _(C)=2*m* (v×Ω)

where:

m: mass of the structure moved

v: velocity of the structure moved

Ω: external yaw rate

The Coriolis force F_(C) causes a deflection Δx in a CVG. The mechanicaltransfer function x/F of the CVG then causes this deflection Δx toundergo a phase shift α when the quality of the mechanical system is notsufficiently high and the frequency difference between the workingfrequency and the resonance frequency of the detection mode is low.

To be able to measure a yaw rate, this signal is demodulated with anin-phase, velocity-proportional signal v_prop. CVGs exhibit interferencesignals that are not proportional to the velocity. Rather, theseinterference signals are in phase with the path and they may possibly bemuch greater than the actual yaw rate signal RATE to be measured. Thedemodulation signal v_prop, which is obtained from the PLL, is thereforealso phase-shifted by α in order to determine the yaw rate precisely andin order not to have components of interference signal QUAD in theoutput signal.

In order to balance the PLL at the band end, demodulation takes place inthe signal path according to QUAD (x_prop), the external yaw rate isapplied and the phase is changed until it is no longer possible toobserve an effect on the signal output by the yaw rate. FIG. 1 showsschematically the circuitry of an implementation of this method.

This method may be applied if the quadrature signals are so small thatthey do not overmodulate the signal path. However, if the interferencesignals are greater than the useful signal by several orders ofmagnitude, then a quadrature control loop is provided. This isimplemented as an extension of the illustration of FIG. 1 in FIG. 2 toillustrate the related art.

The previously described balancing method now fails since when a yawrate is applied and the PLL is incorrectly balanced, the quadraturecontrol loop suppresses the quadrature demodulated yaw rate signal atthe signal output, i.e., the criterion for balancing the PLL is lacking.Rather, the signal at the quadrature controller output is used here as abalancing criterion. Very small V/°(α) signals are produced at theoutput of the quadrature controller which become even smaller if thecapture range of the controller is large. It is not possible to avoidthese problems by strengthening the output of controller output signalUI (see FIG. 2; FIG. 4) since the supply voltage available is usuallylimited and amounts to 5V, for example. The signal for suppressing thequadrature is often substantially greater than the signal produced byapplying a yaw rate. Amplified signal UI would therefore reach thelimits of the possible modulation range.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for balancingthe phase-locked loop of an electronic analyzing device, which analyzesthe output signal of a sensor device such as a yaw rate sensor utilizingthe Coriolis effect in particular, as well as to provide an electronicanalyzing device, the method and the analyzing device making it possiblefor the phase-locked loop of the electronic analyzing device to balancethe phase-locked loop of the electronic analyzing device with a clearlyhigher percentage rate of assigned sensor devices.

As already explained above, in order to suppress deflection-proportionalinterference signals, a quadrature control loop is used in the analyzingdevice to analyze the output signal of a sensor device.

An important aspect of the present invention is that the quadraturecontrol loop is expanded so that the output signal of the controller ofthe quadrature control loop delivers a higher output voltage during thebalancing of the phase-locked loop than during normal control operation.The output signal delivered is a function of the amplitude of theexternal yaw rate acting on the sensor device and phase angle a set inthe PLL. It is thus possible to dimension the capture range of thequadrature control loop for normal control operation in such a way thateven sensor devices having large interference amplitudes may be used.This would not be possible without the change in the control loopaccording to the present invention since the two requirements arecontradictory.

As explained, an electronic analyzing device is assigned to each sensordevice, the phase-locked loop of each analyzing device being balanced tothe specific sensor. Since the electronic analyzing device of thepresent invention and the method of the present invention for balancingthe phase-locked loop allows the possibility for even balancing sensordevices, the output signals of which have a higher interference signal,it is possible to significantly reduce the reject rate ofnon-balanceable sensor devices and accordingly the production costs.

Furthermore, it is an advantage that the method of the present inventionto balance the phase-locked loop can be completely automated with verylittle expense for circuitry and is thus suitable for mass production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a known analyzing device and analyzing circuit for theknown yaw rate sensor which is shown in a highly schematic form.

FIG. 2 shows a known extension of the analyzing circuit in FIG. 1 with aquadrature control loop to suppress strong interference.

FIG. 3a shows an analyzing circuit according to the present inventionfor the known yaw rate sensor, which is shown in a highly schematicform, the switch positions of the switches according to the presentinvention for normal controller operation being shown.

FIG. 3b shows the analyzing circuit according to the present inventionof FIG. 3a, the switch positions of the switches according to thepresent invention for the balancing condition being shown.

FIG. 4 shows the known yaw rate sensor in detail and the known analyzingcircuit according to FIG. 2.

FIG. 5 shows the known yaw rate sensor in detail and the analyzingcircuit according to the present invention according to FIG. 3a.

DETAILED DESCRIPTION

A CVG has a drive loop which is used to cause a seismic mass to vibrate.An electric, path-proportional signal x picked off in the drive loop isused as an input signal for a PLL. Depending on the drive concept, avelocity-proportional signal v may also be processed. The drive loop isnot shown as part of the description of the present invention since thepresent invention refers to the processing of the output signals of aCVG.

FIG. 1 shows a combination 100 of a known yaw rate sensor 3 which isshown in a highly schematic form and a known analyzing device oranalyzing circuit 8, the analyzing device determining the yaw rate RATEOUT from the output signal of the sensor device, i.e., of the yaw ratesensor, i.e., of CVG 3. The yaw rate-proportional Coriolis force F_(C)causes a deflection Δx on the oscillating mass, the deflectionundergoing a phase shift α in relation to Coriolis force F_(C) becauseof the mechanical transfer function x/F of CVG 3 in question. Afterpassing through a C/U converter 5, the output signal of the CVG ispresent as a voltage signal and after passing through an intermediateamplifier 6 having a gain factor g, it is further processed as voltage Uin analyzing device 8. To be able to measure a yaw rate RATE, signal Uis demodulated with an in-phase, velocity-proportional signal.Rectangular signals x_prop and v_prop used for this purpose are providedseparately by a phase-locked loop or PLL 10 from input signals x and α.x_prop is in phase with signal x. v_prop is phase-shifted by 90° inrelation to signal x. The signals are used for in-phase synchronousdemodulation. As a rule, a CVG exhibits interference signals QUAD thatare not proportional to velocity but rather are proportional to and inphase with the path. In addition, the interference signals may possiblybe very much greater than RATE OUT, the yaw rate signal to be actuallymeasured. Demodulation signal v_prop, which is obtained from PLL 10, istherefore also phase shifted by α in order to determine yaw rate RATEOUT precisely and to prevent components of the quadrature signal, i.e.,interference signal QUAD in the output signal. To determine α, inputsignal U of analyzing unit 8 is demodulated in a signal path 12according to QUAD (x_prop) by supplying it in succession to a mixer ormultiplier 13, an amplifier 14, a low-pass filter 15 and an amplifier 16having adjustable gain g_var. Offset balancing takes place at a summer17 so that quadrature signal QUAD may be picked off as a signal at anoutput OUT.

To adjust or balance the device shown, amplified yaw rate signal U ofangular sensor 3 is applied at described signal path 12 and phase angleα is changed until no effect by the yaw rate can be observed at thesignal output. However, this method can only be used if quadraturesignals QUAD are so small that they do not overmodulate signal path 12.If, however, interference signals QUAD are larger by several orders ofmagnitude tha yaw rate signal RATE OUT which is contained and isisolated, then a quadrature control loop 20 is provided. This has beendone as an extension of the illustration of FIG. 1 in the circuit ofFIG. 2. Quadrature control loop 20 includes a first mixer 21 in whichsignal U amplified by a factor g by amplifier 6 is mixed with x_prop toform output signal UI after passage through a controller 22. UI is mixedwith auxiliary signal x_prop provided by PLL 10 once more in a secondmixer 23 and is then sent in inverted form to a summer 25 together withthe still not amplified output signal of CVG 3 in order to eliminate orsubstantially reduce interference signal QUAD.

The balancing method described above with reference to FIG. 1 fails in adevice according to FIG. 2 since quadrature control loop 20 suppressesthe quadrature demodulated by the yaw rate signal at the output if theyaw rate signal of sensor 3 is applied and PLL 10 is incorrectlybalanced. This means that the criterion for balancing phase angle α ofPLL 10 is lacking. Rather, a signal at an output of controller 22 is nowused as a balancing criterion in this case. At the output of controller22, very small V/°(α) signals are produced, which are made even smallerwith a large capture range of controller 22. It is not possible to avoidthese problems by amplifying signal UI at the output of controller 22since the supply voltage available is usually limited to 5V, forexample, and the signal for suppressing the quadrature is oftensubstantially greater than the signal resulting through the effect of anexternal yaw rate. Amplified signal UI would therefore reach the limitsof the possible modulation range.

Some processing steps are explained below in the form of equations toillustrate the problems occurring and the positive effect of a methodand a device according to the present invention:

Provided that v=constant and no path-proportional interference signals(quadrature Q) are present, the following is true:

U=const.1*cos(w 0*t−α)*Ω*cos(wN*t)  (1)

U=1/2*const.1*Ω*[cos((w 0−wN)*t−α)+cos((w 0+wN)*t−α)]

where:

U: amplitude modulated yaw rate-proportional signal

const.1: constant 1

w0: sensor drive resonance frequency

α: phase shift of detection mode of sensor element

Ω: external yaw rate

wN: useful frequency or yaw rate

t: time variable

If during the synchronous demodulation with rectangular signal v_prop,it is disregarded that the odd-numbered multiples also delivercomponents, then if

 v_prop=cos (w 0*t−α)

where:

v_prop: velocity-proportional demodulation signal

RATE OUT=gvar*const.1*1/2*Ω*cos(wN*t)

where:

RATE OUT: output signal at the yaw rate sensor

is obtained as an output signal after low-pass filtering withsuppression of the double frequency:

Using g_var, it is possible to balance the desired sensitivity of entirecombination 300 in amplifier 16.

If quadrature signals Q are present, under the assumption that thequadrature is also phase-shifted by α, then (1) is modified to:

U=const.1*cos(w 0*t−α)*Ω*cos(wN*t)+const.2*Q*sin(w 0*t−α)  (3)

where:

Gvar: variable gain for sensitivity balancing

Q: amplitude of the quadrature signals QUAD

const.2: constant 2

If demodulation signal v_prop were not now shifted by a, the followingwould result:

RATE OUT=gvar*const.1*1/2*Q*cos(wN*t)*cosα+gvar*const.2*1/2*Q*sinα  (4)

It is apparent from equations (3) and (4) that the quadrature signalQUAD component is small compared to the useful signal for two reasons:

1. The signal processing is able to process the quadrature signal in alinear manner until the synchronous demodulation.

2. If there is an incorrect demodulation with angle α, an offset isproduced at the output:

RATE OUT=gvar*const.2*1/2*Q*sinα

Therefore, a quadrature control loop 20 is provided in the system whichpath (quadrature) demodulates amplitude-modulated signal U bymultiplication with x_prop, FIG. 2. This signal is supplied via acontroller 22 which is an I-controller and integrates the signal. Aftera repeated modulation with x_prop, output signal UI is “held against”the quadrature signal coming from sensor element 3 at summer 25. Summer25 reduces the quadrature component of voltage U to zero except for avery small, residual deviation.

FIG. 4 shows the known yaw rate sensor in greater detail and the knownanalyzing circuit according to FIG. 2. For the sake of clarity, only thereference symbols of the major function blocks and connecting elementshave been entered, e.g., CVG 3, analyzing device 8, quadrature controlloop 20, etc.

The capture range of quadrature control loop 20 results in:

ΔUI=ΔUIN=U _(HF) *δC/CQ 1,2

where:

U_(HF): amplitude of the measuring voltage at carrier frequency

ΔUI: change of the I-controller output voltage

ΔUIN: modulator input voltage

i.e., at a given maximum ΔUI (e.g., specified by the maximum range ofthe modulation of the operational amplifier), the maximum allowableδC_(Quad) is:

δC _(Quad) =CQ 1,2*ΔUI/U _(HF)

where:

δC_(Quad): change in capacitance due to quadrature

CQ1,2 coupling capacitance of the quadrature control loop

δC_(Quad) and ΔUI are understood to be the amplitudes of thecorresponding sinusoidal oscillations. From (5), it is apparent that thequadrature controller capture range may also be expanded by enlargingCQ1,2, and a minimum CQ1,2 is used for a capture range.

If PLL 10 has been incorrectly balanced by angle a and if a constantexternal yaw rate proportional to cos(w0*t) is applied for thebalancing, then the amplitude of the controller output is adjusted sothat the controller receives no input signal.

The following trigonometric equation applies:

δC*cos(w 0*t−α)=δC*[cos(w 0*t)*cosα+sin(w 0 *t)*sinα]

The first term in the square brackets is the yaw rate which remainsnearly uninfluenced (for α <1°) by the quadrature control loop. Thesecond term is in phase with the quadrature and is therefore detectedand suppressed by the quadrature control loop.

The following applies to the steady-state condition:

δC+sin(w 0*t)*sinα=CQ 1,2* ΔUI/U _(HF)*sin(w 0*t) or

ΔUI=U _(HF) +δC/CQ 1,2+sinα  (6)

Numerical example:

If U_(HF)=0.8V, CQ1,2=0.75 pF, δC=2.5 fF at 100°/s and α=1°, ΔUI=47μV/°, i.e., in the arrangements shown in FIG. 2 and FIG. 4, a very highvoltage change of 47 μV/° at an external yaw rate of 100°/s ismeasurable at the controller output.

Balancing is carried out in the devices of FIGS. 2 and 4 according tothe related art in such a way that with an applied constant yaw rate,all balancing bits of the PLL balancing are selected and the outputsignal of controller 22 is recorded. The same procedure is repeated withan opposite sign at the same yaw rate. The point of intersection of bothcharacteristics denotes the correct balancing combination. However,small balancing values are difficult to detect during production. Theproblem may be corrected by using an additional amplifier. However, thishas the disadvantage that quadrature signal QUAD present at thecontroller output in any case, which may be much larger than thebalancing signal, is also amplified.

A device according to the present invention to solve this problem isshown in FIG. 3a. Compared to the circuit in FIG. 2, three branches 30,31, 32 have been added to the circuit in FIG. 3a for improved balancing.According to the method described below, the extended circuit ofanalyzing device 8 is added via switches 35, 36 in signal path 12, aswitch 37 in quadrature control loop 20, and one switch 38, 39 each infeedback branch 30 and connecting branch 32. It is possible to changethe switch position of switches marked 35, 36, 37, 38, 39 by a logical“1” via a FLAG RL_QH which may be activated by software duringbalancing. As a result, attenuating branch or tuning branch 31 isconnected between the output of controller 22 and the input of theamplifier or impedance transformer 47. Attenuating branch 31 has anattenuating element 42 which has an attenuation factor K2, a summer 44,a coupling element 46 which supplies the output signal weighted with afactor K1 to summer 44 via feedback branch 30, and an impedancetransformer 47 which is connected between the output of summer 44 andthe input of mixer 23. The input of coupling element 46 is connectedwith RATE OUT; a separate input for this purpose may also be provided inan alterative embodiment. The switch positions in FIG. 3a are drawn asthey apply for RL_QH=0, i.e., the switch position in normal controloperation. FIG. 3b also shows the switch positions for RL_QH=1, i.e.,the balancing state.

According to the present invention, the following method is preferredfor the quadrature adjustment of PLL 10 and analyzing device 8:

1. First, voltage UI is measured and read out at the output ofquadrature controller 22 for the switch positions corresponding toRL_QH=0 without the effect of an external yaw rate. In this way, voltageUI_(Quad) is determined for yaw rate sensor 3 to be balanced, thisvoltage being used to clear the existing quadrature of sensor device 3.

2. By setting RL_QH=1 and the corresponding switch positions, thisvoltage UI_(Qaud) is applied to coupling element K1 via the offsetbalancing, which is present in any case with RATE OUT. Signal path 12 issimultaneously connected to the signal ground or frame via switch 36 inorder only to have the effect of the offset balancing at the signaloutput. Signal UI at the output of controller 22 is set to the signalground or frame, i.e., nothing additional is fed in since the voltageused to suppress the quadrature is already made available via couplingelement K1.

3. If an external yaw rate is now applied, the controller output voltagethus changes according to:

ΔUI=1/K 2*U _(HF) *δC/CQ 1,2*sinα  (7)

where:

ΔUI: change of the controller output voltage

K2: attenuation factor

U_(HF): amplitude of the measuring voltage at carrier frequency

δC change in capacitance of the measuring capacitors in the sensorelement

CQ1,2: coupling capacitances of the quadrature control loop

α:phase shift of detection mode of sensor element

Since K2<<1 may be selected, it is possible to significantly increasethe balancing sensitivity. The correct balancing combination is nowdetermined again as was described above referring to the related artaccording to FIG. 2. CQ1,2 may not fall below a minimum value derivedfrom the quadrature capture range; therefore, the balancing sensitivitymay also increased via 1/K2>>1 with given U_(HF) and δC.

4. After balancing, RL_QH=0 is set by the software and the switchesassume the position shown in FIG. 3a.

The adjustment of the balancing sensitivity is thus decoupled from thequadrature capture range and is carried out with substantially improvedprecision. To complete the method, which may be implemented fullyautomatically, for example by suitable software, the normal controloperation is adjusted in the tuned control device.

FIG. 4 shows a combination 400 of known yaw rate sensor 3, which isshown in greater detail compared to FIG. 1, and known analyzing circuit8 according to FIG. 2. FIG. 5 shows a combination 500 of known yaw ratesensor 3, which is shown in greater detail compared to FIG. 1, and theanalyzing device/analyzing circuit of the present invention according toFIG. 3a. For the sake of clarity, only the reference symbols of themajor function blocks of FIGS. 2 and 3a are indicated in FIGS. 4 and 5.For the implementation of the method of the present invention, it isinconsequential that as a result of the effect of the external yaw rateon the oscillating mass of the sensor, a high frequency voltage U_(HF)is used to analyze the capacitance change of the capacitors C1=C₀+□C andC2=C₀−□C of yaw rate sensor 3, as is indicated in FIGS. 4 and 5.

In a refinement of the present invention, the quadrature voltage isapplied to coupling unit K1 externally via a separate pin or terminal(not shown).

What is claimed is:
 1. A method of balancing a phase-locked loop of anelectronic analyzing device that analyzes an output signal of a sensordevice representing a yaw rate signal, the electronic analyzing deviceincluding an oscillating mass that undergoes a deflection under aneffect of an external yaw rate on the sensor device and the outputsignal, the electronic analyzing device including a control loopprovided with a controller having an input and an output, the controlloop being further provided with one of a modulator and mixer having aninput provided with a first electrical connection to the output of thecontroller, the method comprising: interrupting the first electricalconnection between the output of the controller and the input of the oneof the modulator and the mixer; and producing a second electricalconnection between the output of the controller and the input of the oneof the modulator and the mixer, an attenuating element being connectedin between in the second electrical connection.
 2. The method accordingto claim 1, wherein: the sensor device includes a yaw rate sensoroperating in accordance with the Coriolis effect.
 3. The methodaccording to claim 1, wherein: the control loop includes a quadraturecontrol loop.
 4. The method according to claim 1, further comprising:selecting an attenuation factor of the attenuating element to be lessthan 1, whereby a balancing sensitivity of the output of the controlleris substantially increased compared to when the attenuation factorequals
 1. 5. The method according to claim 1, wherein: the secondelectrical connection is made by connecting a summer in between.
 6. Themethod according to claim 1, wherein: for balancing the phase-lockedloop, the first electrical connection is produced in a first step and anoutput voltage of the controller is determined without an effect of theexternal yaw rate on the sensor device.
 7. The method according to claim6, wherein: for the balancing of the phase-locked loop, the secondelectrical connection is produced in a second step.
 8. The methodaccording to claim 7, wherein: the electronic analyzing device includesan output stage and is connected to signal ground during the secondstep.
 9. The method according to claim 8, further comprising: adjustinga voltage level of the output of the controller to a voltage level ofthe signal-ground during the second step; and supplying a voltage to asummer of the control loop via a summer of the output stage, wherein:the voltage supplied to the summer of the control loop is proportionalto the voltage level of the output of the controller determined in thefirst step.
 10. The method according to claim 9, wherein: the externalyaw rate acts on the sensor device in a third step.
 11. The methodaccording to claim 3, wherein: the following applies to an outputvoltage of the controller under the effect of the external yaw rate:UI=1/K 2*UHF*C/CQ 1,2*sin where: UI: change in the controller outputvoltage, K2: attenuation factor, UHF: amplitude of a measuring voltageat a carrier frequency, C change in capacitance of measuring capacitorsin a sensor element, CQ1,2: coupling capacitances of the quadraturecontrol loop, and : phase shift of detection mode of the sensor element.12. An electronic analyzing device for measuring an output signal of asensor device representing a yaw rate signal, comprising: an oscillatingmass that undergoes a deflection under an effect of an external yaw rateon the sensor device and the output signal; a phase-locked loop; and acontrol loop provided with: a controller having an input and an output,one of a modulator and a mixer having an input, an attenuating element,and at least one of a summer and a coupling element.
 13. The electronicanalyzing device according to claim 12, wherein: the sensor deviceincludes a yaw rate sensor operating in accordance with the Corioliseffect.
 14. The electronic analyzing device according to claim 12,wherein: the control loop includes a quadrature loop.